The present invention relates to a voice analysis composing method, and more particularly to a voice analysis composing method of a phonemic piece editing type.
Generally the voice analysis composing method of a phonemic piece editing type comprises the steps of extracting, in pitch units, the representative phonemic piece data from the raw voice signal in accordance with the strong similarity among the adjacent waveforms of the voiced sound, sequentially connecting the extracted phonemic piece data while repeating the extracted phonemic piece data a plurality of times in accordance with the voiced composition controlling information, and editing the phonemic piece data to compose the desired voice signal. As an example, FIG. 1 shows one portion of the voice signal waveform composed by the voice analysis composing method of a phonemic piece editing type. The signal of FIG. 1 is a voice signal provided by a three-time repetition of the phonemic piece PHA, a connection to the phonemic piece PHB and a two-time repetition of the phonemic piece PHB.
Since the voice analysis composing method of the phonemic piece editing type composes a voice signal by the sequential connection of the phonemic piece data in accordance with the voice composition controlling information, the voice analysis composing method thereof is simplified in its composing procedure as compared with the parameter analysis composing method such as PARCOR system, LSP system, Formant composing system or the like, whereby the voice composition can be easily realized by the use of a general purpose micro-processor or the like.
However, this method had a problem in that periodical noise sounds were caused due to the repetition of the phonemic piece, thus rendering it difficult to provide a smooth voice signal, since the waveforms and the pitch periods of the phonemic piece changed abruptly in the connection point of the different phonemic pieces as shown in FIG. 1.
To improve such problems, the insertion of the interpolation phonemic piece to be provided by the interpolating operation between two phonemic pieces was hitherto proposed.
Namely, the ith data value PHI (i) of the interpolation phonemic piece PHI of the preceding phonemic piece PHA and the succeeding phonemic piece PHB is obtained from the following equation (1), wherein the ith data value of the preceding phonemic piece PHA of the phonemeric piece data group provided by the sampling operation of the voice signal at the given sampling period is assumed to be PHA (i) (i=1, 2, . . . , N.sub.A, wherein the N.sub.A is the data number of the PHA), the ith data value of the succeeding phonemic piece PHB is assumed to be PHB (i) (i=1, 2, . . . , N.sub.B, wherein the N.sub.B is the data number of the PHB), EQU PHI (i)=f{PHA (i), PHB (i)} (1)
In the equation (1), the f (A, B) is the interpolation functions of the two phonemic piece data A, B.
The interpolation of two phonemic piece data is adapted to be obtained by the linear interpolation. Assume that the number of the interpolation phonemic piece to be inserted into between two phonemic pieces is M, and the ith data value PHI (i, j) of the jth interpolation phonemic piece can be obtained from the following equation (2) ##EQU1##
Since the data value PHB (i) of the succeeding phonemic piece can be provided through a condition of (j=M+1) in the equation (2), the PHB can be called an interpolation phonemic piece in a broad sense. Also, assume that M' to be defined in the following equation (3) is called An "interpolation repeating number." The equation (2) can be represented in the equation (4) when the M' is used. ##EQU2## wherein j=1, 2, . . . , M'.
A problem of the conventional method was in the processing method of the phonemic piece data in the calculation of the phonemic piece data of the interpolation phonemic piece in accordance with the equation (1) or the equation (2), since the phonemic pieces were generally different in respective pitch periods and thus the data number N.sub.A of the phonemic piece PHA was different in value from the data number N.sub.B of the phonemic piece PHB. In this case, the phonemic piece data of the interpolation phonemic piece is obtained after the data number of two phonemic pieces has been rendered equal by addition of the final data value or zero data to the phonemic piece data, which has a lower data number.
To obtain the smooth, natural voice signal, the pitch period is required to be smoothly varied. Accordingly, the data number N.sub.I of the interpolation phonemic piece is obtained through an interpolation operation as shown in the equation (5) from the data number N.sub.A of the preceding phonemic piece PHA and the data number N.sub.B of the succeeding phonemic piece PHB. EQU N.sub.I =INT{g (N.sub.A, N.sub.B)} (5)
wherein the g (N.sub.A, N.sub.B) is the interpolation function of two data numbers N.sub.A, N.sub.B, and the INT (x) is the function for rendering x equal to the nearest integer.
The data number of the interpolation phonemic piece is obtained by a linear interpolation. When N is the number of the interpolation phonemic pieces to be inserted between two phonemic pieces, the data number N.sub.I (j) of the jth interpolation phonemic piece is given by the following equation (6). ##EQU3## wherein j=1, 2, . . . , M+1.
Accordingly, the pitch period can be smoothly varied by a method of outputting, by the number of the data obtained by the interpolation, the phonemic piece data obtained as described hereinabove so as to cut off the remaining data.
However, in this method, the remaining data of the interpolation phonemic piece was obliged to be cut off and thus noise was caused due to the cutting-off operation.
FIG. 2, (b) shows as interpolation phonemic piece PHI, obtained from the phonemic piece PHA shown in FIG. 2, (a) and the phonemic piece PHB shown in FIG. 2, (b), by a conventional method.
In FIGS. 2(a)-(c), the interpolation phonemic piece PHI is a phonemic piece to be inserted into the middle portion of the phonemic piece PHA and the phonemic piece PHB. The data value and the data number of the interpolation phonemic piece are both obtained by a linear interpolation.
Since the final data value of the interpolation phonemic piece is not zero as shown in FIG. 2, (b), this fact causes the noise sounds.
In FIG. 2(a)-(c), .tau. is the clock period when the data is sampled, i is the sample data number, t is time, N.sub.A and N.sub.B are respective data numbers of the phonemic pieces PHA and PHB.